What does metazoa mean?
Metazoa is the scientific name for the great branch of life containing multicellular animals, including humans, insects, worms, molluscs, fishes, birds, and mammals. In traditional classification it forms a kingdom separate from the sponges, although modern evolutionary studies treat Metazoa as a clade within the broader kingdom Animalia. Its members are distinguished from unicellular organisms by cellular organization and, in most cases, by the presence of true tissues. The group displays enormous variation in body form, from simple and radially symmetrical animals to complex creatures with bilateral symmetry, specialized organs, and sensory systems. Metazoa is also important in evolutionary biology because comparisons among its members reveal which anatomical and molecular features were inherited from a common ancestor and which evolved independently. Outside formal classification, the term is especially associated with research into animal development, phylogeny, and the origin of multicellularity.
noun (taxonomic name, plural in form)Metazoa is the biological clade comprising multicellular animals, generally ranked as a kingdom and traditionally distinguished from the sponges. It includes all major animal groups from simple tissue-bearing forms to vertebrates such as humans.
- The taxonomic clade consisting of multicellular animals, traditionally excluding sponges and usually treated as a kingdom or its equivalent.
"The study of cellular specialization and development in Metazoa has revealed the common biological foundations shared by diverse animals."
"Complex nervous systems are among the most striking features found in Metazoa."
"Fossils have revealed new branches of Metazoa that were previously unknown."
Metazoa is itself a plural taxonomic name and has no standard plural form.
"The earliest known fossils provide evidence about the earliest Metazoa."
Every human being is a metazoan: the name belongs to a family tree that ultimately joins us to animals as different as jellyfish and insects.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does metazoa come from?
Metazoa was formed in the early 19th century from Greek meta-, meaning 'after' or 'beyond', and zōa, a plural form of zōion meaning 'animal'. The name reflected the historical idea that true multicellular animals arose after simpler organisms traditionally grouped as protozoa. Its components also appear in related scientific terms such as zoology, zoologist, and protozoon.
Related word forms
How metazoa is actually used
Metazoa is a formal taxonomic name and is normally used unchanged and in the plural, as with other names for animal clades. In less technical contexts, animals or Animalia may be used instead.
Easily confused with metazoa
Metazoa generally includes animals characterized by organized tissues, whereas Parazoa traditionally refers to animals such as sponges that lack true tissues and organs.
Protozoa are primarily single-celled eukaryotes, while Metazoa refers to multicellular animals.